1. Field of the Invention
The present invention relates generally to the art of venetian blinds and window shades, and more specifically to a system in which lifting cords and cord locking mechanisms are eliminated. Still more specifically, the invention relates to window covering systems which employ one or more consistent, variable force springs to continuously compensate for the weight of accumulated window covering material, depending upon the extent to which the blind or shade is raised or lowered.
2. Description of the Prior Art
Venetian blinds have been known for many years and typically include a plurality of slats made from metal, wood or other materials and supported by spaced apart ladders. Such blinds typically include a bottom bar and a tilt mechanism to cause the slats to move from a horizontal position to a nearly vertical position to open and close the blinds with respect to the passage of light. It is also conventional with such systems to use lifting cords coupled to the bottom bar, passing through the slats and into mechanisms within the blind headrail. The cord is used to raise the bottom bar, accumulating individual slats as the bar is raised. Because of the natural tendency of the bar and accumulated slat weight to free fall, locking mechanisms are also commonly employed with such prior art devices.
Several attempts have been made to eliminate the lifting cord locks, some of such attempts going back nearly 140 years, i.e., Bixler, U.S. Pat. No. 13,251, issued Jul. 17, 1855 for "Inside Blinds." In this device, a pair of "fusees" are employed, namely spirally grooved pulleys, to wind the lifting cord. The two fusees are arranged so that as a spring is being wound about a wider diameter portion of one, it is being unwound from a smaller diameter portion of the other, with a spool provided for accumulation of the lifting cord.
U.S. Pat. No. 2,420,301, issued May 13, 1947 to Cusumano for "Venetian Blind" also employs a cone-shaped member with grooves and an elongate coil spring. This design dispenses with normal draw cords and provides a counterbalance so that the slats may be retained at any vertical position without a lock or anchorage and so that the blinds can be raised with relatively small effort.
A different device is shown in Pratt's U.S. Pat. No. 2,324,536 issued Jul. 20, 1943 for "Closure Structure." In this device, tapes and coil springs are employed to raise and lower a blind particularly suited for use in a vehicle such as a train. The complex structure disclosed in this patent is especially suitable for devices in which the bottom bar and the slats ride in tracks as they move upwardly and downwardly.
Other patents show various spring devices used with venetian blinds. For example, in Cohn's U.S. Pat. No. 2,390,826, issued Dec. 11, 1945 for "Cordless Venetian Blinds," two coil springs are used to provide even force, with a centrifugal pawl stop. The blind is raised by freeing the pawl to allow the spring to provide a lift assist. Other more conventional systems employing springs and ratchet and pawl mechanisms include those shown in Etten's U.S. Pat. No. 2,824,608, issued Feb. 25, 1958 for "Venetian Blind"; U.S. Pat. No. 2,266,160, issued Dec. 16, 1941 to Burns for "Spring Actuated Blind"; and U.S. Pat. No. 2,276,716, issued Mar. 17, 1942 to Cardona for "Venetian Blind."
None of the aforementioned patents disclose the use of consistent variable force springs to eliminate the conventional pull cords and locks of venetian blinds in a simple and easily adaptable mechanism having few components parts. Similar problems also exist in the window shade field. A system which overcomes the disadvantages of the more complex and cumbersome systems of the prior art would represent a significant advance in this art.